Cardiac MRI: The Study That Shows Scar, Inflammation, and Infiltration

The Scene

The following scene is drawn from the composite of patients I have cared for in clinic and on the hospital floor. All identifying details are changed.

He was thirty-eight years old when his echocardiogram came back with an ejection fraction of 32 percent. Three weeks earlier he had been running five miles on Saturdays. No chest pain, no prior hospitalizations, no known cardiac history. What he had noticed was that he was tired in a way that sleep did not fix, and that he had needed to stop midway through a climb of two flights of stairs, something that had never happened before.

The echo showed a dilated left ventricle, global hypokinesis, and mild mitral regurgitation. The pattern was consistent with dilated cardiomyopathy. What it could not tell me was why. Was this ischemic cardiomyopathy from a silent MI in a man who had never been to a cardiologist? Was it viral myocarditis that had burned out? Was it a genetic cardiomyopathy? Was it alcohol-related or toxin-related? Was it sarcoidosis? Each of these answers has a different treatment trajectory and a different prognosis.

The cardiac MRI answered the question.

The late gadolinium enhancement pattern showed mid-myocardial fibrosis in a patchy, non-ischemic distribution: not in the territory of a single coronary artery, not subendocardial, but in the mid-wall of the septum and lateral wall. That pattern is most consistent with prior myocarditis or genetic cardiomyopathy, not ischemic disease. The coronary arteries were normal on CTA. The right ventricular morphology and function were intact. T1 mapping showed increased native T1 values in the septum consistent with fibrosis.

What we had was not a mystery anymore. We had a map. The treatment changed, the prognosis calculation changed, and the genetic counseling conversation became necessary. The MRI did not cure anything. But it told us what we were treating, and that is irreplaceable information.

Cardiac MRI is available at Carle Foundation Hospital in Urbana-Champaign through a dedicated CMR program with fellowship-trained interpretation. In cases requiring specialized cardiac MRI protocols for infiltrative disease or complex congenital evaluation, patients can be referred to Northwestern Medicine Bluhm Cardiovascular Institute in Chicago or the University of Illinois Health cardiac imaging program.

What It Is

Cardiac magnetic resonance imaging (CMR, also called cardiac MRI) uses strong magnetic fields and radiofrequency pulses to generate images of the heart without ionizing radiation. Unlike echocardiography, which reflects sound waves off tissue interfaces, MRI measures the behavior of hydrogen nuclei (primarily in water and fat) as they absorb and release radiofrequency energy. Different tissues have different magnetic relaxation properties, and those differences produce image contrast.

What cardiac MRI measures:

• Cardiac chamber dimensions and volumes with high spatial precision (considered the reference standard for biventricular volumes and ejection fraction) 5 / Solid 01064-2)
• Wall motion abnormalities, with higher spatial resolution than echocardiography
• Myocardial perfusion during stress with adenosine or regadenoson (CMR perfusion imaging)
• Late gadolinium enhancement (LGE): the distribution and pattern of fibrosis or scar following gadolinium contrast injection
• Native T1 mapping: a quantitative measure of tissue composition reflecting fibrosis, edema, or infiltration, without contrast
• T2 mapping: a quantitative measure of myocardial free water content, reflecting edema and inflammation
• T2*: a measure sensitive to iron deposition, used in hemosiderosis and transfusion-dependent conditions
• Flow quantification: blood flow volume across valves and septal defects using phase-contrast imaging
• Pericardial anatomy and constraint

What makes CMR unique: No other single imaging modality provides simultaneous structural, functional, and tissue characterization data in a single study. Echocardiography assesses structure and function but cannot characterize myocardial tissue composition. Nuclear imaging assesses perfusion and function but cannot characterize fibrosis. Coronary CTA images the coronary arteries with precision but provides limited myocardial tissue information. CMR does all of these things, and in several clinical scenarios, it provides information that no other test can replicate.

Gadolinium contrast and late gadolinium enhancement: Gadolinium-based contrast agents distribute in the extracellular space. In normal myocardium, the extracellular space is small and gadolinium is rapidly cleared. In fibrotic or necrotic tissue, the extracellular space is expanded, gadolinium accumulates in higher concentrations, and it washes out slowly. Ten to fifteen minutes after injection, a sequence called inversion recovery fast gradient echo nulls the signal from normal myocardium while the abnormal tissue appears bright. This is late gadolinium enhancement (LGE), and its distribution pattern is the most diagnostically specific tool in cardiac imaging for distinguishing ischemic from non-ischemic disease 5 / Solid .

The Mechanism

The physics of MRI in brief: Hydrogen nuclei in tissue align with a strong external magnetic field. A radiofrequency pulse disturbs this alignment. As the nuclei relax back, they emit signals that are spatially encoded by gradient magnetic fields and reconstructed into images. The two primary relaxation times, T1 (longitudinal) and T2 (transverse), depend on the molecular environment of the hydrogen nuclei. Tissue with different water content, fat content, fibrosis, or iron deposition has different T1 and T2 values, creating the tissue contrast that makes CMR so informative.

Cardiac gating: The heart moves continuously. CMR acquires data over multiple cardiac cycles, synchronizing data collection to the ECG signal and reconstructing a representative single cycle from the averaged data. This requires a regular cardiac rhythm; atrial fibrillation and frequent ectopy degrade image quality and may make certain sequences non-diagnostic.

LGE pattern interpretation: The distribution of late gadolinium enhancement is diagnostically specific because it reflects the mechanism of tissue injury:

• Subendocardial or transmural LGE in a coronary territory: Ischemic scar from prior MI. The enhancement follows the distribution of a coronary artery because MI affects the innermost layer (endocardium) first, working outward (the “wavefront phenomenon”). 5 / Solid
• Mid-myocardial or epicardial LGE not following a coronary territory: Non-ischemic fibrosis. This pattern is seen in myocarditis, genetic cardiomyopathies (including LMNA, PLN, desmin mutations), cardiac sarcoidosis, and hypertrophic cardiomyopathy.
• Diffuse subendocardial LGE: Cardiac amyloidosis. The gadolinium kinetics are globally abnormal, and the normal myocardium may be difficult to null, producing a distinctive “zebra stripe” or “global null difficulty” pattern.
• Patchy LGE in a patient with hypertrophy: Hypertrophic cardiomyopathy (HCM). The distribution and extent of LGE in HCM correlates with arrhythmic risk.
• No LGE in a patient with reduced ejection fraction: An important finding. It suggests idiopathic dilated cardiomyopathy without scar, which has a different response to therapy and a better prognosis than ischemic cardiomyopathy with comparable EF.

T1 mapping: Native T1 mapping (without contrast injection) quantifies T1 relaxation times across the myocardium. Increased native T1 is seen in conditions that expand the extracellular space: fibrosis, edema, amyloid infiltration. Reduced native T1 is seen in iron overload and Anderson-Fabry disease (lysosomal lipid storage within cardiomyocytes). Post-contrast T1 mapping allows calculation of the extracellular volume fraction (ECV), which quantifies the proportion of myocardium occupied by extracellular matrix, a direct measure of diffuse fibrosis 4 / Promising .

T2 mapping: T2 relaxation time increases when free water content increases. In acute myocarditis, the inflamed myocardium has increased T2. In edema surrounding an acute MI, the jeopardized but viable tissue shows increased T2 surrounding the core of necrosis (the “area at risk”). T2 mapping is therefore a marker of acute inflammation or ischemia, in contrast to LGE which marks established necrosis or fibrosis.

How It Is Used

Cardiomyopathy evaluation: This is the dominant clinical use. When a patient presents with unexplained reduced ejection fraction, CMR is the study that distinguishes ischemic from non-ischemic etiology, identifies specific non-ischemic patterns (myocarditis, sarcoidosis, amyloidosis, HCM, ARVC), and quantifies scar burden. The management pathways for these diagnoses diverge completely. Ischemic cardiomyopathy drives evaluation for revascularization. Myocarditis with significant LGE drives ICD consideration. Cardiac sarcoidosis drives corticosteroid therapy and aggressive ICD implantation. Amyloidosis drives disease-specific therapies including ATTR stabilizers. None of these distinctions can be made from the ejection fraction or the echo alone.

Viability assessment before revascularization: In patients with ischemic cardiomyopathy who are being considered for CABG or PCI, CMR LGE quantifies the transmurality of scar in dysfunctional segments. Segments with less than 50 percent transmural LGE are more likely to recover function after revascularization (hibernating myocardium). Segments with 75 to 100 percent transmural LGE are replaced by scar and will not recover regardless of revascularization. This information guides the decision to revascularize versus medical management in patients with severe LV dysfunction 4 / Promising .

Suspected myocarditis: The Lake Louise Criteria, updated in 2018, provide a standardized framework for CMR diagnosis of myocarditis. A combination of regional or global T2 elevation (edema marker) and LGE in a non-ischemic pattern meets criteria for an acute myocardial injury consistent with myocarditis 5 / Solid . In patients with chest pain, increased troponin, normal coronary arteries on invasive angiography or CTA, and a clinical picture suggesting viral illness, CMR frequently confirms active myocarditis and guides the recommendation for activity restriction, which is critical in a condition where exertion can precipitate lethal arrhythmia.

Hypertrophic cardiomyopathy risk stratification: In HCM, the amount and distribution of LGE predicts the risk of sudden cardiac death. Patients with extensive LGE (greater than 15 percent of LV mass) have a significantly higher rate of ventricular arrhythmias and sudden death, informing ICD implantation decisions 4 / Promising .

Arrhythmogenic right ventricular cardiomyopathy (ARVC): CMR is the imaging modality of choice for evaluating RV structure in suspected ARVC. RV wall motion abnormalities, focal RV aneurysms, and fatty infiltration of the RV wall (though fat assessment on CMR must be interpreted carefully) contribute to the task force criteria for ARVC diagnosis.

Cardiac sarcoidosis: CMR with LGE demonstrates patchy, multifocal enhancement in a distribution that is non-ischemic and often involves the basal septum and lateral wall. This pattern, in combination with FDG-PET imaging, is central to the diagnosis and treatment monitoring of cardiac sarcoidosis, a condition that carries a high risk of complete heart block and sudden cardiac death 4 / Promising .

Cardiac amyloidosis: CMR shows diffuse subendocardial LGE, abnormal gadolinium kinetics with difficulty nulling normal myocardium, and increased native T1 and ECV consistent with extensive extracellular protein deposition. These findings, combined with the clinical presentation and SPECT bone tracer imaging (for ATTR amyloidosis), confirm the diagnosis without the need for endomyocardial biopsy in many cases 5 / Solid .

CMR perfusion stress imaging: Myocardial perfusion CMR uses first-pass gadolinium kinetics during pharmacologic vasodilation stress (adenosine or regadenoson) to identify territories of reduced perfusion. Compared with nuclear SPECT, CMR perfusion has higher spatial resolution and avoids ionizing radiation. In the CE-MARC trial, CMR had higher diagnostic accuracy than SPECT for detecting significant coronary artery disease 5 / Solid 61335-4).

The Evidence

STICH Trial and Viability Substudy

The Surgical Treatment for Ischemic Heart Failure (STICH) trial randomized 1,212 patients with coronary artery disease and ejection fraction below 35 percent to CABG plus medical therapy versus medical therapy alone. The main trial showed a significant reduction in all-cause mortality with CABG over ten years (HR 0.84; 95% CI 0.73 to 0.97; p = 0.02) 5 / Solid .

The STICH viability substudy evaluated whether myocardial viability assessment (by SPECT or dobutamine echo) predicted benefit from CABG. The substudy’s striking finding was that viability did not predict differential survival benefit from CABG versus medical therapy in multivariable analysis, challenging the long-standing assumption that viability testing should guide revascularization decisions 5 / Solid .

However, the STICH viability substudy used SPECT and dobutamine echo, not CMR. CMR LGE provides transmurality information that those techniques do not. Several observational data show that CMR transmurality of scar predicts functional recovery after revascularization with higher specificity than nuclear viability techniques, even if the survival data from a CMR-specific RCT do not yet exist 4 / Promising .

CE-MARC Trial

The CE-MARC trial enrolled 752 patients with suspected coronary artery disease and compared CMR (including perfusion, wall motion, and LGE) versus SPECT for detecting greater than 70 percent stenosis on invasive angiography 5 / Solid 61335-4).

Results:

• CMR sensitivity: 86.5 percent
• SPECT sensitivity: 66.5 percent
• CMR specificity: 83.4 percent
• SPECT specificity: 82.6 percent
• CMR had significantly higher sensitivity (p less than 0.0001) without significant difference in specificity

CMR detected coronary artery disease with higher diagnostic accuracy than SPECT, using no ionizing radiation, and the addition of LGE information contributed to the performance advantage.

LGE and Prognosis

The prognostic significance of LGE in dilated cardiomyopathy was evaluated in a meta-analysis of 29 studies with 7,578 patients. The presence of LGE was associated with significantly higher risk of all-cause mortality (HR 2.37; 95% CI 1.94 to 2.90), sudden cardiac death or appropriate ICD therapy (HR 2.71; 95% CI 1.98 to 3.70), and heart failure hospitalization 5 / Solid .

In a landmark study of 472 patients with non-ischemic dilated cardiomyopathy, mid-wall fibrosis on LGE was present in 26 percent of patients and was independently associated with a two-fold higher risk of sudden cardiac death or ICD discharge over a median 5.3-year follow-up (HR 2.43; 95% CI 1.50 to 3.92) 5 / Solid . This finding has influenced ICD indication discussions in patients with non-ischemic cardiomyopathy and EF in the 35 to 45 percent range where guideline-based ICD indications are less clear.

MINOCA and CMR

Myocardial infarction with non-obstructive coronary arteries (MINOCA) affects approximately 5 to 10 percent of patients presenting with acute MI. CMR in MINOCA patients identifies the underlying etiology (myocarditis, Takotsubo syndrome, microvascular obstruction, coronary spasm with MI pattern) in 60 to 80 percent of cases, changing management in a substantial proportion 5 / Solid . Without CMR, many MINOCA patients are discharged with the diagnosis of “unclear” MI, missing conditions that are treatable and have distinct prognoses.

Gadolinium Deposition Concerns

Gadolinium-based contrast agents approved for cardiac use include linear and macrocyclic formulations. Evidence has emerged that gadolinium deposits in brain tissue (particularly the dentate nucleus) after repeated exposures, even with normal renal function 3 / Early . This finding has prompted regulatory review. No neurological symptoms attributable to gadolinium brain deposition have been confirmed in patients with normal renal function. Macrocyclic agents have lower deposition than linear agents in animal and human studies and are preferred for repeat examinations 4 / Promising .

Gadolinium must not be given to patients with GFR below 30 mL/min/1.73 m² without careful risk-benefit assessment due to the risk of nephrogenic systemic fibrosis (NSF), a rare but severe fibrosing condition associated primarily with older linear agents 5 / Solid . NSF has become exceedingly rare since the replacement of high-risk linear agents.

Non-contrast CMR protocols using native T1, T2, and T2* mapping, along with cine imaging, provide substantial diagnostic information without gadolinium and are increasingly used in patients with renal insufficiency or those requiring multiple repeat examinations.

The Patient Experience

Before the Scan

CMR is a longer study than echocardiography or CT. A standard full cardiac MRI takes 45 to 90 minutes. Patients with gadolinium protocols should inform the ordering team of renal function (a recent creatinine is typically required). Patients with metallic implants must be screened carefully: most modern pacemakers and defibrillators now have MRI-conditional labels, but older devices and certain abandoned leads require specialist review before scanning. Hip and knee replacements from titanium or cobalt-chromium alloys are generally compatible but may produce local artifacts.

The magnet itself is a large bore cylinder, typically 1.5 or 3 Tesla. The bore diameter is approximately 60 to 70 cm, which is substantially wider than older scanner designs but still provokes claustrophobia in roughly 2 to 5 percent of patients. Patients who know they have significant claustrophobia should request anxiolytic premedication before scheduling. Open MRI systems produce substantially lower image quality and are not adequate for cardiac imaging.

No ionizing radiation is involved.

What Your Cardiologist Will Not Have Time to Explain

The CMR report contains multiple numbers that the interpreting cardiologist uses to make decisions, but what gets communicated to the patient is often a summary sentence. What is not explained:

• The difference between EF measured by CMR (the reference standard for volume calculation) and EF estimated by echocardiography (accurate in most cases but subject to geometric assumptions that fail in distorted ventricles)
• What LGE means for prognosis, not just for diagnosis. A report that says “mid-wall LGE in the septal wall” is not the same as “normal MRI.” It means fibrosis is present. It changes the arrhythmic risk calculation.
• The difference between “no LGE identified” and “normal myocardium.” No LGE means no detected fibrosis. It does not mean no functional abnormality or no cardiomyopathy.

Pharmacologic Stress CMR

For CMR perfusion studies, adenosine or regadenoson is infused intravenously during the scan. Adenosine causes coronary vasodilation within seconds of infusion and commonly produces flushing, dyspnea, chest pressure, and a brief sensation of heart pounding. These symptoms are expected, predictable, and resolve within 30 to 90 seconds of stopping the infusion. Adenosine is cleared from the body within minutes. Regadenoson is given as a single bolus injection rather than a continuous infusion and has a more favorable side-effect profile for most patients.

Aminophylline is kept at hand to reverse adenosine-induced bronchospasm in patients with reactive airway disease, which is the primary contraindication to adenosine stress.

Sex Differences

Women with unexplained heart failure and preserved ejection fraction (HFpEF) or mid-range ejection fraction represent a population in whom CMR frequently provides the diagnosis when echocardiography and coronary angiography are unrevealing. Cardiac amyloidosis, which has historically been thought of as predominantly a disease of older men, affects women with distinct features including earlier presentation with HFpEF and carpal tunnel syndrome 4 / Promising . CMR T1 mapping and ECV quantification are central to staging amyloid severity in both sexes. Myocarditis following mRNA vaccination presents more commonly in young men, but CMR-confirmed myocarditis in young women following viral illness is well-documented and frequently misattributed to anxiety or musculoskeletal pain 4 / Promising .

Geographic Access

Not every imaging center offers full cardiac MRI with full tissue characterization sequences (T1 mapping, T2 mapping, LGE, and perfusion). Advanced cardiac MRI programs require fellowship-trained readers and specialized hardware. In Illinois, Carle Foundation Hospital offers cardiac MRI with dedicated interpretation. Northwestern Medicine Bluhm Cardiovascular Institute and Rush University Medical Center in Chicago offer complete CMR programs including advanced mapping and stress perfusion. OSF Saint Francis Medical Center in Peoria offers standard cardiac MRI. Patients with complex cardiomyopathy diagnoses requiring advanced CMR should confirm the specific capabilities of their imaging center before scheduling.

Decisions and Trade-Offs

CMR Versus Echocardiography: When Does CMR Add Information?

Echo is faster, less expensive, more widely available, and suitable for serial follow-up in most patients. CMR is the appropriate choice when:

• The echocardiographic windows are poor and accurate volumetric assessment is required
• The etiology of cardiomyopathy is unclear after standard workup
• Tissue characterization is needed (fibrosis, edema, infiltration, iron)
• Viability assessment before revascularization is needed
• Arrhythmic risk stratification in cardiomyopathy requires scar quantification
• Diagnosis of ARVC, HCM, myocarditis, amyloidosis, or sarcoidosis is being considered

For routine EF monitoring in a patient with known ischemic cardiomyopathy on stable medical therapy, echocardiography is sufficient. CMR adds cost and time in that context without changing management for most patients.

The ICD Decision and LGE

The guideline threshold for primary prevention ICD implantation in non-ischemic dilated cardiomyopathy is an EF of 35 percent or less after at least three months of guideline-directed medical therapy. CMR LGE data show that patients with an EF of 36 to 45 percent who have mid-wall LGE may have a higher arrhythmic risk than patients with an EF below 35 percent without LGE. This has created a clinical tension between the guideline threshold (based on EF alone) and the CMR-informed risk estimate. The DANISH trial, which randomized non-ischemic cardiomyopathy patients to ICD versus standard therapy, showed no overall mortality benefit from ICD in the group overall, but a trend toward benefit in those under age 68 5 / Solid . The integration of CMR LGE into ICD decision-making is an active area of guideline evolution 3 / Early 33042-X).

CMR Versus Nuclear Imaging for Ischemia

For detection of obstructive coronary artery disease in symptomatic patients, CMR perfusion and SPECT nuclear imaging have comparable specificity but CMR has higher sensitivity in most comparative studies. CMR avoids ionizing radiation, provides tissue characterization, and offers higher spatial resolution. The primary advantages of nuclear imaging are wider availability, better performance in obese patients (PET over SPECT), and the substantial long-term outcome data from large nuclear registries. For a 45-year-old woman who will need repeat functional imaging over the next 20 years, the cumulative radiation advantage of CMR is clinically meaningful.

The Three Questions Every Patient Should Ask

1. “What does the LGE pattern tell you about the cause of my heart muscle problem?” The LGE distribution is the diagnostic fingerprint of the cardiomyopathy. Ask specifically whether the pattern is ischemic (subendocardial or transmural in a coronary territory) or non-ischemic, and what non-ischemic diagnoses the pattern is consistent with. This drives the downstream workup.

2. “Does the amount of scar on this MRI change whether I need a defibrillator?” LGE extent is now incorporated into ICD risk models. If you have a borderline ejection fraction (35 to 45 percent), the scar burden may push the conversation toward or away from ICD implantation. Ask directly.

3. “Does this scan require gadolinium contrast, and if so, what does my kidney function have to be?” If your eGFR is below 45 mL/min/1.73 m², gadolinium carries risk and the protocol may need to be modified or substituted with native mapping sequences. This needs to be discussed before the day of the scan, not while you are on the table.

Clinical Synthesis

Cardiac MRI is the study that distinguishes the stories that look the same on the surface. Two patients, both with an ejection fraction of 30 percent. One has subendocardial scar in the LAD territory: prior MI, coronary revascularization is the question. The other has mid-wall septal LGE in a non-ischemic distribution: possible LMNA mutation, genetic counseling is the question, and the coronaries are normal. Same number, completely different clinical imperative.

The framework treats CMR as a precision tool, not a routine surveillance test. It is not ordered because the patient is anxious about their heart. It is ordered because a specific diagnostic question cannot be answered by the available data, and the answer will change the plan.

For patients who have been told they have “cardiomyopathy of unclear cause,” a structured cardiovascular assessment includes a structured review of prior imaging to determine whether CMR has been obtained and whether the LGE pattern has been formally characterized. A substantial proportion of patients with this diagnosis have never had CMR, and their treatment has been generic heart failure management rather than etiology-specific therapy. The audit identifies this gap.

For patients with borderline EF and a question about ICD implantation, the clinical review includes CMR scar quantification as part of the risk stratification analysis. For patients with known HCM or suspected infiltrative cardiomyopathy, CMR is built into the cardiovascular workup pathway before any management decisions are made.

OSF Saint Francis Medical Center in Peoria and the University of Illinois Health system are accessible referral points for patients in central Illinois who need cardiac MRI and do not have local access. Rush University Medical Center and Northwestern Medicine Bluhm Cardiovascular Institute provide advanced CMR capabilities for complex cases requiring specialized mapping sequences or combined CMR-PET evaluation.

The scan takes 60 to 90 minutes. The information it provides can redirect a treatment plan that has been running in the wrong direction for months or years.

Paired Foundations Articles:

• PROC-013: Stress Testing (CMR perfusion as an alternative to nuclear stress)
• PROC-016: ICD and Pacemaker Implantation (LGE guides ICD decisions)
• PROC-008: EP Study (arrhythmia mapping in scar-based cardiomyopathy)
• PROC-003: CABG (viability assessment before surgical revascularization)

The Signal Check is fifteen questions mapping the cardiovascular risk pattern across the physiological domains most commonly missed in standard screenings. It produces a specific starting point for your next clinical conversation.